This invention relates to a printing press, for example, a printing press in which ink is circulated from a reservoir into an ink chamber where it is retained under pressure in engagement with a rotating cylinder and returned through a return conduit to the reservoir, and more particularly, to an ink sealing assembly for a printing press of this type.
A printing press of the type for which the ink sealing assembly of the present invention is adapted is disclosed in U.S. Pat. No. 4,497,250, issued Feb. 5, 1985. In this press, the ink chamber is accommodated in an ink fountain, and a doctor blade and ink dam are clamped in the ink fountain. The doctor blade and the ink dam define the upper and lower ink barriers for the ink chamber. The ink is supplied to the ink chamber under pressure and the ink is applied to the surface of the rotating inking cylinder as it passes in open communication with the ink chamber.
Ink seals are provided at both ends of the ink fountain to prevent ink from leaking from the ink chamber to the unused surfaces at the extreme ends of the cylinder. Such leakage of ink will not only foul and damage the equipment, but the cylinder will sling the ink outwardly unless the slinging of the ink is retained by a shield and retained within the confines of the press.
There are occasions when more than one color of ink is run in the fountain. On these occasions, the ink chamber will be divided into sections which apply different ink colors to the cylinder. This fountain arrangement is referred to as a "split" fountain where there are pairs of end seals for each color. These seals must not allow a color from one section to leak into a color of an adjacent section. Moreover, the seal widths must be narrow enough to fit within the margins between pages.
The ink seals must be able to provide an effective seal against three independent movable surfaces, namely, the outer periphery of the rotating cylinder, the doctor blade which engages the cylinder surface and is bendable and deflectable along its length and the ink dam which also flexes as it engages the cylinder. The ink seals must not interfere with the doctor blade setting.
The prior ink sealing arrangements for printing presses of this type have included (1) seals which overlap the ends of the cylinder, (2) seals which engage the outer surface of the cylinder and the end edges of the doctor blade and the ink dam, and (3) individual seals which close off the area at the ends of the ink chamber and engage the cylinder, doctor blade and ink dam. None of these sealing arrangements has proven entirely satisfactory.
The arrangement (1) above is plagued with leakage problems, particulary, leakage through the gap between the seal and the cylinder. Moreover, due to the tendency of the cylinder to sling ink, it requires an ink retainer and shield. It is critical to install since the gaps must be maintained, and it cannot be used for intermediate seals in split fountains.
The arrangement (2) above also has its leakage problems, particularly, leakage between the doctor blade and the seal. Also, as the pressure increases within the fountain, leakage occurs through the seal causing slinging of ink by the cylinder. The arrangement also requires an ink retainer to catch the ink slung by the cylinder, but even so, the arrangement produces troublesome clean-up problems.
The arrangement (3) above results in leakage under the seal, particularly, as the ink pressure is increased. Moreover, it is not adapted to split fountain arrangements. Also, if ink leaks through the seal, this results in the slinging of ink by the cylinder. If the seal is rigid, it will interfere with the doctor blade setting.
The ink sealing assembly of the present invention embodies an inner pressure barrier in communication with the ink chamber, at least one ink seal spaced apart from the pressure barrier on the side remote from the ink chamber, both having sealing edges contoured to engage the doctor blade, the ink dam and the outer periphery of the cylinder intermediate the doctor blade and the ink dam, and means establishing communication between the space or spaces intermediate the sealing edges and the return conduit to the reservoir.
The pressure barrier maintains the pressure within the ink chamber, and at the same time meters a discharge of ink from the ink chamber to the space intermediate the pressure barrier and the ink seal from which the ink returns to the reservoir through the return conduit. A pressure drop is thereby produced so that the ink seal does not have to resist the full pressure within the ink chamber.
In a preferred embodiment of the ink seal assembly of the present invention, the sealing arrangement includes a plurality of spaced apart flexible ink seals in which the edges engaging the doctor blade and the cylinder are deflected toward the ink cylinder so that the pressure within the ink chamber will tend to deflect them against the surface of the doctor blade and cylinder and increase the effectiveness of their sealing action.
The ink seal assembly of the present invention provides an effective seal for the ink chamber within the fountain. It eliminates leakage and ink slinging by the cylinder and the need for additional components, such as ink retainers and shields. Since the seals and pressure barrier are preferably flexible, they tend to self-adjust during wear and do not interfere with the doctor blade setting. Moreover, due to the flexibility and the ink metering capability of the pressure barrier, a more uniform pressure and ink flow can be maintained across the ink chamber, and pressure build-up in the ink blockage will be minimized.
A further advantage of the ink seal assembly of the present invention is that because it can be readily bolted to the ink fountain at the ends of the ink chamber or at other positions across the length of the ink chamber, it can be readily used for split fountains to provide seals between the different color inks.